Pituitary hormones released during sexual maturation of the rat appear to influence the rate of retinal degeneration after exposure to continuous photoperiod. Retinas of young rats prior to sexual maturity are more resistant to damage by radiant energy than those after sexual maturity (6 to 8 weeks of age). The greatest degree of degeneration occurred in the photoreceptor cells (rods and cones), while the bipolar neurons and ganglion cells are only slightly, if at all, structurally affected. Preliminary studies from this laboratory have shown that hypophysectomy (HYPEX), which inhibits sexual maturation and influences other pituitary target organs, exerts a "protective influence" on retinas exposed to continuous radiant energy; the retinas of HYPEX rats do not degenerate as rapidly as those of adult, intact rats. Other preliminary studies have shown a relationship between ovarian hormones and retinal degeneration. These interesting observations related to the effects of pituitary and ovarian hormones on photically-induced retinal degeneration will be examined further in HYPEX and intact rats of different ages after the administration of pituitary extracts and pituitary gonadotrophins; early ovarian maturation will be induced with gonadotrophic hormones. Additional studies will involve retinal degeneration after ovariectomizing rats of different ages and ovarian hormone replacement therapy prior to exposure to either cyclic photoperiod, low-intensity visible radiant energy, or high-intensity radiant energy.